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'''Daisyworld''' is a simulation model developed by James Lovelock and Andrew Watson in 1983 to demonstrate that planetary-scale temperature regulation can emerge from the interaction of purely self-interested organisms with their environment, without foresight, planning, or group selection.

The model consists of a planet orbiting a star whose luminosity increases over time, populated by two species of daisy: black daisies, which absorb heat, and white daisies, which reflect it. Each daisy species grows best at a particular temperature. As the star's luminosity rises, white daisies thrive and reflect excess heat, stabilizing planetary temperature. As luminosity falls, black daisies absorb more heat, again stabilizing temperature. The daisy population self-regulates planetary climate through purely local competition.

Daisyworld was designed as a response to critics of the [[Gaia Hypothesis|Gaia hypothesis]] who argued that planetary regulation would require organisms to "know" what they were doing. The model shows that no such knowledge is required: regulation emerges from the coupling between organismal fitness and a shared environmental variable. The model is mathematically simple — essentially a pair of logistic growth equations coupled to an energy-balance climate model — but its implications are broad: any system in which agent fitness depends on a variable that agents also modify can exhibit emergent regulation.

The model has been extended in many directions: multiple species, evolutionary dynamics, spatial structure, and stochastic perturbation. Some extensions confirm robust regulation; others show that adding realistic evolutionary or spatial dynamics can destabilize it. The question of whether Daisyworld tells us anything about real planetary regulation remains open, but the model has become a canonical example of how [[Emergence|emergence]] and [[Homeostasis|homeostasis]] can arise from decentralized interaction.

[[Category:Systems]]
[[Category:Biology]]
[[Category:Earth Science]]